This invention relates to wireless communication systems, and more particularly to enhance reacquisition of the network within wireless communication systems.
Cellular telephones may operate under a variety of standards including the code division multiple access (CDMA) cellular telephone communication system as described in TIA/EIA, IS-95, Mobile station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System, published July 1993. CDMA is a technique for spread-spectrum multiple-access digital communications that creates channels through the use of unique code sequences. In CDMA systems, signals can be and are received in the presence of high levels of interference. The practical limit of signal reception depends on the channel conditions, but CDMA reception in the system described in the aforementioned IS-95 Standard can take place in the presence of interference that is 18 dB larger than the signal for a static channel. Typically, the system operates with a lower level of interference and dynamic channel conditions.
In current CDMA systems, mobile stations acquire the pilot signal of a base station. The pilot signal has identifying spreading code used by the mobile station. The mobile stations use the pilot signal to synchronize themselves with the base station so the mobile stations can recognize any of the other channels necessary. Once a mobile station acquires the pilot signal of a base station, the mobile station may communicate with the base station over the appropriate channels of the wireless communication system.
After completing a call, or upon call release, the mobile station currently resynchronizes with the base station using the sync channel. Under strong signal conditions, this poses no problems. However, when the signal conditions deteriorate, the mobile station may be unable to resynchronize with the pilot base station. What is needed is a system that allows resynchronization under strong signal conditions but allows for reacquisition when signal conditions deteriorate.
The present invention creates a more robust reacquisition process for the mobile station. The mobile station performs an evaluation of the signal conditions from the base station. The mobile station may perform this evaluation at the end of a call, upon release, or immediately after release. If the signal is strong, the mobile station will jump directly back to the synchronization channel. However, if the signal has deteriorated, the mobile station may determine it is more appropriate to reacquire the pilot signal of a base station. The mobile station may also use the signal characteristics to determine whether to perform a full acquisition, a quick acquisition, or a wide acquisition. The mobile station may also use a history to assist in the reacquisition process.
One aspect of the invention is a method of reacquisition in a wireless communication system. The method comprises obtaining a metric indicating of signal conditions and comparing the metric to a first predetermined threshold. If the metric meets or exceeds the first predetermined threshold, the method attempts connection with the synchronization channel. If the metric does not meet the first predetermined threshold, the method performs reacquisition. The method may also compare the metric to a second predetermined threshold and attempt narrow reacquisition if the metric meets or exceed the second predetermined threshold.
Another aspect of the invention is a method of enhancing reacquisition in a wireless communication system. The method comprises determining signal strength and connecting to the synchronization channel if the signal strength meets or exceeds a first threshold. The method then performs narrow reacquisition if the signal strength is between the first threshold and a second threshold. If the signal strength is at or below the second threshold, the method performs full reacquisition. The method may further creating a history log of reacquisition performance and determine the first threshold and the second threshold using historical data in the history log.
Another aspect of the invention is a mobile station for use in a wireless communication system. The mobile station comprises a signal quality indicator which determines signal quality. A reacquisition logic circuit then determines the appropriate reacquisition procedure based on the signal quality.